This invention relates in general to brake systems for vehicles and in particular to a pump assembly with a combination reciprocating high-pressure seal and fluid inlet check valve for use within brake systems.
In conventional vehicular brake systems having anti-lock brake, traction control and/or vehicle stability control, a supply of hydraulic fluid for the vehicle brakes is modulated by a hydraulic control unit. Various hydraulic pumps may be employed to selectively supply hydraulic fluid to the vehicle brakes. Several hydraulic pump designs are known.
U.S. Pat. No. 4,556,261 to Farr, discloses a prior art pump and skid sensing assembly for a vehicle hydraulic anti-skid braking system, as shown in FIGS. 1 and 2. The assembly comprises a housing 1 incorporating a hydraulic pump 2, and a solenoid-operated valve assembly 3. Only the operation of the pump 2 will be described herein, as the operation of the rest of the anti-skid braking system is not relevant to the present invention. The pump 2 includes a plunger 10, which reciprocates within a stepped bore 11 in the housing 1. The plunger 10 is engageable with a drive mechanism comprising a ring 12 rotatable on a shaft 4. The plunger 10 carries an ‘O’ ring seal 18 and a lip seal 19. The seals 18 and 19 are disposed on opposite sides of a passage 20 leading to the valve 3. The seals 18 and 19, the plunger 10, and the bore 11 define a chamber 22. A reservoir 35 supplies the chamber 22 with fluid.
The seal 19, which is illustrated in detail in FIG. 2, comprises an annular ring of elastomeric material, which is received in an annular groove 25 in the plunger 10. The groove 25 is parallel sided and is of an axial length greater than the thickness of the seal 19. Opposite faces 26 and 27 of the seal 19 are respectively planar and of reduced area, with the face 27 of reduced area being provided with at least one diametrical slot 28 which communicates with one or more passages 29 in the inner peripheral edge of the seal 19. The planar face 26 is adapted to seal against the adjacent, inner, face 25a of the groove 25 to prevent flow from the secondary chamber 22 into the reservoir 35 when the seal 19 is in a first position relative to the plunger 10. The face 25a is formed by an inlet flange 40 of the plunger 10. Thus, the face 26 of the seal 19 and the inlet flange 40 form a check valve assembly for separating the secondary chamber 22 and the reservoir 35. The seal 19 is rather complex in that it contains at least one radial slot 28 and at least one longitudinal passage 29 formed therethrough to permit fluid flow past the check valve assembly when the face 22 of the seal 19 abuts the adjacent side wall of the groove 25.
An inlet passageway 41 is formed by the inlet flange 40 and the housing 1. A retaining flange 42 and the housing 1 form an outlet passageway 43 of the check valve assembly. As the plunger 10 is moved towards the ring 12, the seal 19 moves to a second position relative to the plunger 10 so that the face 26 is spaced apart from the adjacent side wall of the groove 25 and the inlet flange 40. In the second position, the seal 19 may abut the retaining flange 41. This allows fluid from the reservoir 35 to be drawn into the increasing volume of the chamber 22 past the seal 19. When the seal 19 is in the second position, the longitudinal passageway 29 is not in direct communication with the outlet passageway 43. When the seal 19 is in the second position, the longitudinal passage 29 is in fluid communication with the inlet passageway 41, and the longitudinal passage 29 is in fluid communication with the radial slot 28. The radial slot 28 is in fluid communication with the outlet passageway 43, such that the check valve assembly is in an open position and the chamber 22 and the reservoir 35 are communicably connected. Therefore, the radial slot 28 allows the longitudinal passageway 29 to be in indirect fluid communication with the outlet passageway 43. The radial slot 28 has an outer radius that extends beyond the outer radius of the longitudinal passage 29 taken about a longitudinal axis of the plunger 10.
As the plunger 10 is moved in the opposite direction, the face 26 of the seal 19 seals against the adjacent face of the groove 25 so that fluid cannot flow between the plunger 10 and the seal 19 or through the slot 28 and the at least one passage 29 within the seal 19. The seal 19 in this condition thus provides a seal between the plunger 10 and the wall of the bore 11, closing the check valve assembly, and allowing the plunger 10 to pump fluid from the secondary chamber 22 into the primary chamber 23.